The Philosophy of the Weather Part 18

Recent observations also have shown that the storms on the west coast of Central America, and the eastern Pacific, pursue a N. W. course, precisely as in the West Indies, and every where over the surface-trades of the northern hemisphere. Indeed _Mr. Redfield himself has recently investigated several of them, and admits their course to be north-westerly_. (See American Journal of Science, new series, vol. xviii.

p. 181.)

But, suppose the co-existence of the winds and the course of the storms admitted as claimed, let us seek for clearer views. What do these gentlemen mean? Do they intend to have us believe the air has inherent moving power, and that the "tendency" of which they speak is an attribute of the winds, and that when they thus meet, and "come into each other,"

"encounter," or "over-slide," and become acquainted, they wheel into a waltz, and move off northward, "integrally," with unceasing circular movement, even until they arrive at the Arctic circle? Or is it a mere mechanical effect of meeting, "coming into each other," or "over-sliding?"

If the latter, why a tendency to rotation from right to left? The trade-winds, at least, are _continuous, unbroken sheets_, and not disconnected portions which meet and blow past each other, and there is no warrant for placing them _side and side_, and attributing to them any such mechanical effect, and as little respecting the other winds. Outside of the fanciful hypothesis, there are no facts to show such a tendency one way rather than the other; and, in accordance with the known facts regarding stratification of the currents of air, no such "tendency" can exist.

But what _power_ impels the winds, which thus meet at these points? If they be impelled, is it consistent with the action of this power that the _winds_ it has _created_ and _controls_, should thus a.s.sume an _opposite "tendency,"_ and whirl away to the north-eastward, regardless of the power that originated and controls them? What must this "_tendency_" be, which thus _occasionally_ not only diverts the winds from the _usually regular course_ given them by their originating power, but increases their action, from gentle, ordinary winds, to hurricanes? Nay, which gives them a new, resistless gyratory and electric energy, increasing as the new, independent, supposed cyclonic organization moves off, "_integrally_,"

away from "the home of its many fathers," on a devastating journey towards the north pole?

And, further, if all this were true as to the West Indies and Central America, what is to be said of the billions of other storms, originating on a thousand other portions of the earth's surface, and how are they to be accounted for, inasmuch as such other "meetings," "coming into each other," and "over-sliding," and "tendency to deflection," is not a.s.sumed to exist?

These questions cannot be satisfactorily answered. The distinguished theorists are mistaken. The stratus-cloud does not over-lie or cover the storm. IT IS THE STORM. The winds beneath, whether surface or superimposed, are but its incidents, due to its static induction and attraction. Their _direction_ depends on the shape of the storm cloud, and its course of progression, and the susceptibility of the surface atmosphere in this direction or that, to its inductive and attractive influence. Their _force_ to its depth, its contiguity to the earth, and the intensity of its action; and the scud, are but patches of condensation, occasioned by the same inductive action which affects and attracts the surface current in which they form.

Another objection to Mr. Redfield's theory of gyration is based upon the fact that in order to const.i.tute his _storm_, to get the _gyration_, he has to include, at least, an equal amount, generally a great deal more, of _fair weather_. The N. W. wind, the "posterior, or dry side of the gale,"

as he calls it (in the foregoing extract), is a _fair weather wind_. It is _necessary_, however, to complete the supposed _circle_, and it is _pressed into the service_. The practical answer given to the question, "_what are storms?_" is, they are cyclones, part storm, so called, and _part fair weather_; that is, the stratus-cloud, the scud, the easterly wind, and rain or snow of day before yesterday, were the _wet side_, or front part of the storm, and the suns.h.i.+ne, clear sky, and N. W. wind of yesterday, to-day, and, perhaps, to-morrow, are the posterior or dry side.

When a storm clears off from the N. W. it is not _over_, it is, perhaps, _just begun_; and, inasmuch as it storms again, very soon after the wind changes back from the N. W. to the southward, in winter, our weather then is pretty much all _storms_.

The statement of this claim seems so absurd that it may appear like injustice to make it. But gyration can not be made out without it, and it is evident in the extract quoted above; in the claim that the winter northers of the Mexican Gulf are parts of pa.s.sing storms; and clearly and unequivocally advanced as a distinct proposition, as follows:

"1. The body of the gale usually comprises an area of rain or foul weather, together with another, and, perhaps equal, or greater, area of fair or bright weather." (Am. Jour. of Science, vol. xlii. p. 114.)

Now, in the first place, we must distinguish between a storm and fair weather, before we can tell what the former is, and it is difficult to a.s.sent to a theory which explains what a S. E. storm of _twelve hours'_ continuance is, by including _two or three days of succeeding N. W. fair weather wind_, as a part of it. There is no proportionate relation as to _time_, nor any relation as to _qualities_, or the attending conditions of the atmosphere, nor any conceivable _connection_, except the hypothetical one of _gyration_, between the two winds.

And, in the second place, it is true, and Mr. Redfield is well aware of the fact, that winds often blow for many days from the N. E., S. W., or N.

W., without any preceding or succeeding winds to which they have any discoverable relation. If, therefore, truth would justify Mr. Redfield in including the fair weather wind, a difficulty would remain which his theory does not cover or explain.

No American, except Mr. Redfield, has been able to discover satisfactory evidence of the gyration of storms, by actual careful observation, or a careful unbiased collation of the observation of others. Professor Coffin is reported to have read to the Scientific a.s.sociation, at their Buffalo meeting, a paper, confirmatory, in part, but I have not been able to see it. The tracks of tornados have been searched as with candles. When they have been narrow, from forty to eighty rods, their action has been substantially similar, and, although, as we have herein before stated, some irregularities have been found which were consistent with gyration--for irregularities attend the violent action of all forces, and particularly the motion of electricity through the atmosphere, as every one who has seen the zig-zag course of a flash of lightning knows--yet the evidence of two lateral inward currents, or lines of force, has predominated over all others. In all cases, where the path is narrow, those lateral currents are the actors; they const.i.tute the tornado; their _irregularities_ of action produce the exceptions; but the exceptions are neither numerous nor uniform, and do not prove either the theory of Mr.

Espy or that of Mr. Redfield. The action is not that of moving air, merely, but of a power exceeding in force that of powder, which nothing but electricity or magnetism can exert. As the path widens, the wind becomes more like the straight-line gust which follows beneath the ordinary severe thunder-showers. His theory finds no substantial confirmation or support in the path of the tornado.

Several storms were investigated by Professor Espy, some of them the same which Mr. Redfield had attempted to show were of a rotary character; one or two by the Franklin Inst.i.tute of Philadelphia; one by Professor Loomis, already alluded to; and recently, two by Lieutenant Porter, from logs returned to the National Observatory. None of these investigations confirm the theory of Mr. Redfield. Indeed, Mr. Redfield himself has found it necessary to resort to suppositions of _modifying causes_ to explain the evident inconsistencies. It is a.s.sumed that the axis, or center, oscillates, and describes a series of circles; and thus, one cla.s.s of difficulties is avoided. Again, it is a.s.sumed that simultaneous storms converge and blend upon the same field, and another cla.s.s of difficulties are surmounted. And, again, inasmuch as it is notorious that violent gales are rarely if ever felt with equal violence around the area of a circle, but from one or two points only, it is a.s.sumed, that the storm winds ascend, superimpose, and descend again, when they return to the place of their first violent action, etc. The _simple truth_ requires no such resort to _modifying hypothesis_.

Still, another objection is, that the changes in the barometer, which occur before, during, and after storms, do not sustain the claims of Mr.

Redfield or the requirements of his theory.

The barometer sometimes rises before storms. It generally commences falling about the time, or soon after the storm sets in, continues to fall during its progress, and rises again, sooner or later, afterward. This is the general rule.

On this subject Mr. Redfield's claim is this:

"EFFECT OF THE GALE'S ROTATION ON THE BAROMETER.--The extraordinary fall of the mercury in the barometer, which takes place in gales or tempests, has attracted attention since the earliest use of this instrument by meteorologists. But I am not aware that the princ.i.p.al cause of this depression had ever been pointed out, previously to my first publication in this journal, in April, 1831, when I took the occasion to notice this result as being obviously due to the _centrifugal force_ of the revolving motion found in the body of the storm.

"Since that period, inquiries have been continued by meteorologists in regard to the periodical and other fluctuations of the barometer, and the relations of these fluctuations to temperature and aqueous vapor. But these incidental causes of variation, in the atmospheric pressure, prove to be of minor influence, and we are left to the sufficient and only satisfactory solution of this marked phenomenon which is found in the centrifugal force of rotation."

The average pressure of the atmosphere, at the surface of the ocean, or in the interior of the country, allowing for elevation, is about equal to the weight of a column of quicksilver, thirty inches in height; hence the barometer is said to stand at about thirty inches at the level of the sea.

This is sufficiently accurate for the northern hemisphere, north of the N.

E. trades; but the average is somewhat lower in the trades and in the southern hemisphere. Thus, the average of sixteen months, during which the Grinnell expedition was absent, was 30.08/100.

From a large number of logs examined by Lieutenant Maury, the mean elevation in the N. E. trades of the Atlantic was 29.97/100; the S. E.

trades of the Atlantic, 29.93/100; off Cape Horn, 29.23/100; S. E. trades of the Pacific, 30.05/100; N. E. trades of the Pacific, 29.96/100. The height of the barometer off Cape Horn is not a fair index of the general elevation of the southern hemisphere, inasmuch as it stands lower there than at the coast of Patagonia and Chili, or at most, if not all, other stations in that hemisphere.

As the barometer is constantly oscillating up and down (irrespective of its diurnal oscillation), it has no known fair weather standard. The point of 30 inches is taken only as it is a mean. I have known it to commence storming when the barometer was at 30.70, and not to fall before it cleared off, below 30.30. And I have known it to be below 30 for several days consecutively, with fair weather. In our climate there is no reliable fair weather standard for the barometer. It falls below 30 without storming; it rises far above, and storms without falling below. No reliance can be placed upon its elevation, except by comparison; but of that hereafter.

The general rule, nevertheless, is, that it falls more or less during storms, whatever its height, and rises sooner or later, more or less, after they clear off.

The difference between its highest and lowest points is called its range.

The greatest range observed, and recorded, is about 3 inches--from about 28 to 31--but this range is rare. The range, in the trade-wind region, is comparatively small; in this country it is greater than in Europe; and, generally, the range will be found greatest where the volume of counter-trade, and magnetic intensity, and the corresponding amount of precipitation, and extremes of heat and cold are greatest. One of the greatest ranges during one storm, or two successive portions of a storm, in this country, which I have seen recorded, occurred at Boston, in February, 1842. It was as follows--counting the hours as 24, and from midnight:

Feb. 15..10h..30.36.

" 16..13h..28.47 fall of 1.89 in 27 hours.

" 17..19h..30.39 rise of 1.92 in 30 hours.

" 18.. 2h..30.39 stationary 5 hours.

" 19.. 2h..29.46 fall of 0.93 in 24 hours.

" 20.. 2h..30.43 rise of 0.97 in 24 hours.

Amount of oscillation, 5.71 in 4 days, 11 hours.

These ranges were owing to the alternation of S. E. storms, and N. W.

winds.

Taking the first range as a basis, and allowing the height of the atmosphere to be 1,100 feet for the first inch, we have nearly 2,000 feet displaced during one day, if we look for the displacement near the earth, or some 30 or 35 miles, if we soar aloft in the upper regions to look for the _lateral overflow_ of Professor Dove, and about the same quant.i.ty restored the next. This brings us to the inquiry, how was it done? It is perfectly idle to talk about _difference_ of _temperature_ or _tension_ of _vapor_, the _ascent_ of warm air, or _descent_ of cold in a case like this; or to say that they were occasioned by a lateral overflow of some thirty miles of its upper portion, first this way and then that, in such a brief s.p.a.ce of time. The change is equal to nearly 1/15 of the weight of the whole atmosphere, and the cause, whatever it was, existed within two or three miles of the earth. Mr. Redfield's explanation I give in his own words, at length:

"One of the most important deductions which may be drawn from the facts and explications which are now submitted, is an explanation of the causes which produce the fall of the barometer on the approach of a storm. This effect we ascribe to the centrifugal tendency or action which pertains to all revolving or rotary movements, and which must operate with great energy and effect upon so extensive a ma.s.s of atmosphere as that which const.i.tutes a storm. Let a cylindrical vessel, of any considerable magnitude, be partially filled with water, and let the rotative motion be communicated to the fluid, by pa.s.sing a rod repeatedly through its ma.s.s, in a circular course. In conducting this experiment, we shall find that the surface of the fluid immediately becomes depressed by the centrifugal action, except on its exterior portions, where, owing merely to the resistance which is opposed by the sides of the vessel, it will rise above its natural level, the fluid exhibiting the character of a miniature vortex or whirlpool. Let this experiment be carefully repeated, by pa.s.sing the propelling rod around the exterior of the fluid ma.s.s, in continued contact with the sides of the vessel, thus producing the whole rotative impulse, by an external force, a.n.a.lagous to that which we suppose to influence the gyration of storms and hurricanes, and we shall still find a corresponding result, beautifully modified, however, by the quiescent properties of the fluid; for, instead of the deep and rapid vortex before exhibited, we shall have a concave depression of the surface, of great regularity: and, by the aid of a few suspended particles, may discover the increased degree of rotation, which becomes gradually imparted to the more central portions of the revolving fluid. The last-mentioned result obviates the objection, which, at the first view, might, perhaps, be considered as opposed to our main conclusion, grounded on the supposed equability of rotation, in both the interior and exterior portions of the revolving body, like that which pertains to a wheel, or other solid. It is most obvious, however, that all fluid ma.s.ses are, in their gyrations, subject to a different law, as is exemplified in the foregoing experiment; and this difference, or departure from the law of solids, is doubtless greater in aeriform fluids than in those of a denser character.

"The whole experiment serves to demonstrate that such an active gyration as we have ascribed to storms, and have proved, as we deem, to appertain to some, at least, of the more violent cla.s.s; must necessarily expand and spread out, _by its centrifugal action, the stratum of atmosphere subject to its influence, and which must, consequently, become flattened or depressed by this lateral movement, particularly toward the vortex or center of the storm_; lessening thereby the weight of the inc.u.mbent fluid, and producing a consequent fall of the mercury in the barometrical tube. This effect must increase, till the gravity of the circ.u.mjacent atmosphere, superadded to that of the storm itself, shall, by its counteracting effect, have produced an equilibrium in the two forces. Should there be no overlaying current in the higher regions, moving in a direction different from that which contains the storm, the rotative effect may, perhaps, be extended into the region of perpetual congelation, till the medium becomes too rare to receive its influence. But whatever may be the limit of this gyration, its effect must be to _depress_ the _cold stratum_ of the upper atmosphere, particularly toward the more central portions of the storm; and, by thus bringing it in contact with the humid stratum of the surface, to produce a permanent and continuous stratum of clouds, together with a copious supply of rain, or a deposition of congelated vapor, according to the state of the temperature prevailing in the lower region."

The italics in the foregoing extract are mine; and, in relation to it, I observe:

1st. There is no cylindrical vessel around storms, and _air will not thus resist air_. Confessedly, such resistance is necessary. Let any one watch his cigar smoke, and see how readily it moves on, with little momentum.

Let any one try the experiment of creating a whirl in the _open air_, or in a room, or box of paper, or other material, which can be suddenly removed, with air colored by smoke. I am exceedingly mistaken if he does not find the presence of a "cylindrical vessel," absolutely essential to prevent the instantaneous tangential escape of the air.

2d. Turn back to page 3 and look at the fall of the barometer in the polar regions (recorded in the extract from Dr. Kane), with _scarcely any wind_, and _as little variation_ in its _direction_, and see how utterly Mr. Redfield's theory fails to account for the phenomena.

3d. If I understand Mr. Redfield correctly, he has abandoned the claim as originally made, that the wind moves in circles, expanding, and _spreading out_ by a "_lateral movement_," and now a.s.serts that it blows spirally inward, and elevates the air in the center. I quote:

"VORTICAL INCLINATION OF THE STORM WIND.--By this is meant some degree of involution from a true circular course. In the New England storm above referred to, this convergence of the surface-winds appeared equal to an average of about 6 from a circle. In the present case, such indication seems more or less apparent in the arrows on the storm figures of the several charts, where the concentrical circle afford us means for a just comparison of the general course of wind which is approximately shown by the several observations.

"Perhaps we may estimate the average of the vorticose convergence, as observed in the entire storm for three successive days, at from 5 to 10--out of the 90 which would be requisite for a congeries of _centripetal_ or center-blowing winds. This rough estimate of the degree of involution is founded only on a bird's-eye view of the plotted observations. But, however estimated, this involution seems to afford a measure of the air and vapor which finds its way to a _higher elevation_ by means of the vortical movement in the body of the storm."

If the elevation of the air at the borders of the storm, and depression in the middle, resulted from the outward tendency and "lateral movement" of the revolving air, and from the _centrifugal force_, as in the experiment with the water in a cylindrical vessel, as stated in the first paragraph quoted, an _involution_ of from 5 to 10 from the action of a _centripetal force_, must carry the air _inward_, and the _barometer should stand highest in the middle of the storm_. The change is fatal to his theory. The two are diametrically opposite in character and effect. In one, the superior strata would be brought down in the center by the _lateral pressure outward_; in the other, they would be elevated by the _involution_, which "affords a measure of the air and vapor which finds its way to a higher elevation," etc. It is perfectly obvious Mr. Redfield has refuted his own hypothesis.

In doing this, he is met by the other difficulty alluded to, which he does not attempt to explain. This gathering of the air inward, spirally, by a centripetal force, if it took place, not only would not depress, but _must elevate the barometer in the center, above that of the adjoining atmosphere_.

When he first attributed the depression of the barometer to a lateral movement and centrifugal force, he supposed the superior strata descended into the depression, and their frigidity occasioned the condensation, and cloud, and rain. How he now proposes to account for the formation of cloud and rain during storms, while the warm air of the inferior stratum finds its way to a higher elevation in the center of the storm, he does not inform us, and we must wait his time.

"I have," he says, "long held the proper inquiry to be, _what are storms_? and not, _how are storms produced_? as has been well expressed by another. It is only when the former of these inquiries has been solved that we can enter advantageously upon the latter."

The former does not seem to be yet solved, or the solution of the latter commenced. Mr. Redfield tells us (page 259, and onward), that there is an extended stratum of stratus-cloud, which overlies the storm, and that it does not differ greatly from one mile in height. We are not told how the air, which finds its way to a higher elevation during several days continuance of such a storm, _gets through the stratum_. If he is right it _must_ do so, and it would not answer to _suppose_ a very small opening or gentle current through it, to carry off all the air which works inward in a hurricane, during several days continuance. But he does not seem to recognize either the necessity or existence of any _vent_ at all; nor is there any; and this fact is open to the observation of every school-boy in the country; and it is equally open to his observation that _when and where the barometer is most depressed, the stratus storm-cloud is nearest the earth_. Colonel Reid has much to say about the "_storm's eye_," or "treacherous center" of a storm. A careful a.n.a.lysis of the instances where the "storm's eye" is noticed will show that the term is applied, in the northern hemisphere, to that lighting up in the W. or N. W., which is the commencement of the clearing-off process, and attended with a s.h.i.+ft of wind to the fair-weather quarter: _i. e._, to W. or N. W. Just such an "eye" as is seen when the last of the storm cloud has pa.s.sed so far to the east as to admit the rays of the sun under the western or north-western edge of it. The same kind of "storm's eye" is described in the southern hemisphere, except that the wind s.h.i.+fts to S. W. instead of N. W., that being the clearing-off wind there. No instance of a "_storm's eye_" in the center of the extended stratum of stratus-cloud, which overlies the storm, can be found recorded, to my knowledge; and it is obvious that Colonel Reid adopts the view of Mr. Redfield, that the westerly and N. W.

_fair weather_ winds are a part of the storm. So long as these gentlemen hold to that opinion they will never solve the question, "_what are storms?_" or reach the other, "_how are storms produced?_"

Notwithstanding, Mr. Redfield a.s.serts, or adopts the a.s.sertion, that the inquiry should be, "What are storms?" not "How are storms produced?" that inquiry should be a _rational_ one, and should not violate all a.n.a.logy, or call for an explanation which science can not _rationally_ furnish. Mr.